David Cameron has been accused of "misleading the public" over the Maria Miller expenses scandal.

In an interview with Sky News, the Prime Minister said that independent members on Parliament's Standards Committee - and not MPs - had made the "casting vote" on how the Culture Secretary should be dealt with after an expenses investigation.

He said that MPs had not been allowed to "police themselves" after it emerged that the committee, which is made up of cross party politicians alongside lay members, had downgraded the amount Mrs Miller should be asked to repay.

Labour MP John Mann, who initially reported Mrs Miller to the Parliamentary Commissioner for Standards, said: "This is the man who said he wanted to clean up politics. Clearly he doesn't understand the system of self regulation and has mislead the public.

"He should write a letter to Maria Miller to inform her she is leaving the Cabinet."

Video:Minister's 30-Second Sorry Moment

Downing Street admitted the Prime Minister had made a mistake in suggesting lay members had made the decision on Mrs Miller's treatment.

Mrs Miller has kept her job after issuing a 32-second apology on Thursday for over-claiming thousands on a second home and her poor attitude to the sleaze watchdog's expenses investigation.

She was asked to repay just £5,800 in expenses she had wrongly claimed for a second home after the 10-member standards committee overruled the standards commissioner's findings that she should pay back £45,000.

Speaking during a visit to Devon, Mr Cameron said: "MPs aren't policing themselves, we have now got a committee that has independent members on and effectively they had the casting vote and what this committee has decided - and it's not my decision it's the committee's decision - they decided that Maria Miller had not done what she was accused of doing.

"They cleared her of that, they found that she had made mistakes that she herself admitted to and actually helped to discover so they asked her to repay money, which she has done, and they asked her for an apology, which she has made."

When asked if he had treated her differently because she was a woman, he said: "I am not treating Maria Miller any differently from anyone else in the Cabinet."

The Labour MP Thomas Docherty has now written to the Metropolitan Police asking it to investigate Mrs Miller's expenses claims.

Mr Cameron's comments came after his spin chief Craig Oliver was forced to deny attempting to quash the story about Mrs Miller's expenses by threatening a newspaper editor.

She has always denied using her oversight of the reforms to press regulation suggested in the Leveson report in a bid to threaten The Daily Telegraph into backing off the story.

However, the newspaper's former editor Tony Gallagher has said that not only did Mrs Miller's special adviser threaten a reporter but the Prime Minister's official spokesman also phoned him.

Video:PM: 'Lay Members Made Miller Call'

Mr Gallagher told Radio 4's Today Programme: "I then got a third call from [the Downing Street communications director] Craig Oliver, pointing out that she's looking at Leveson and the call is badly timed."

The Daily Telegraph first raised the issue of the involvement of Mr Oliver in December 2012, at the height of the growing scandal surrounding the Tory MP for Basingstoke's expenses.

However, on Friday Mr Oliver responded saying: "It is entirely false to suggest that I tried to threaten him with Leveson in any way.

"The conversation I had with him was about the inappropriate door-stepping of an elderly man (Maria Miller’s father)."

Mrs Miller was reported to the Parliamentary Commissioner for Standards by Mr Mann in December 2012 over concerns she had improperly claimed around £90,000 on a southwest London property between 2005 and 2009.

On Thursday a standards committee report cleared Mrs Miller of wrongly claiming, ruling she was entitled to the allowance on the Wimbledon second home she sold in February for a £1.2m profit.

She was told to repay £5,800 she said were as a result of changes to her mortgage payments caused by falling interest rates, which she had not reflected in her claims.

She was also told to apologise to the House of Commons for her attitude to the investigation, which the report had concluded was unhelpful.